2025 NYJC H2 Chem Hydroxy Compounds Tut Ans SECTION A

1 Nanyang Junior College Chemistry (9729) Tutorial 14 Hydroxy Compounds Prepared by Mrs Judy Tan JC2/2025 Section A: Self-Check Questions Part 1: Alcohols 1 For the following compounds given by their IUPAC name, draw their skeletal formula. (i) Propan-1,3-diol OH OH (ii) Phenylmethanol OH 2 Below is a cyclohexane derivative. OH State the type of reaction and draw the structural formula of the organic product(s) formed by the action of the reagents stated below: (a) HCl (g) (b) Acidified dichromate(VI) ions CH3 Cl Type of reaction: nucleophilic substitution CH3 O Type of reaction: oxidation (c) Na metal (d) Concentrated H2SO4 at 170oC CH3 O - Na + Type of reaction: reduction CH3 CH3 (major) (minor) Type of reaction: elimination

2 3 There are four structural isomers of C4H9OH. The structure of one isomer, 2-methylpropan-2-ol, a tertiary alcohol is shown below. HO C CH3 CH3 CH3 (i) Draw the structures and give the names of the other three isomers of C 4H9OH. Classify each as either primary, secondary or tertiary. isomer CH3CH2CH2CH2OH CH3CH(OH)CH2CH3 CH3 C CH3 CH2 OHH name butan-1-ol butan-2-ol 2-methylpropan-1-ol classification primary secondary primary (ii) One of the isomers gives a positive test with alkaline aqueous iodine. Identify the isomer and write a balanced equation for the reaction. The isomer is CH3CH(OH)CH2CH3, (butan-2-ol). CH3CH(OH) CH2CH3 + 4I2 + 6NaOH  CHI3 + CH2CH3CO2Na+ + 5NaI + 5H2O (iii) 2-methylpropan-2-ol could be distinguished from the other two isomers by a simple chemical test. State the test and give the observations. test: To each sample, add potassium dichromate(VI), H2SO4 (aq) and heat Observations: 2-methylpropan-2-ol (Tertiary alcohol): Orange potassium dichromate(VI) remains Butan-1-ol & butan-2-ol: Orange potassium dichromate(VI) turns green Continue on the next pg

3 (iv) One of the isomers of C4H10O exhibit the following:  It exists as a pair of isomers.  3 alkenes are formed when it is heated with Al2O3. Identify the alcohol, including your reasoning. The alcohol is CH3CH(OH)CH2CH3. (butan-2-ol)  It exists as a pair of enantiomers as it contains a chiral carbon. C CH2CH3 CH3 OH H C CH2CH3 CH3OH H  It undergoes elimination with Al2O3 to form the 3 alkenes: C C H H H CH2CH3 C C H CH3 H CH3 C C CH3 H H CH3 But-1-ene cis but-2-ene trans but-2-ene

4 4 Complete the following summary of reactions for a secondary alcohol, propan-2-ol. (Compare this summary with the one for a primary alcohol – pg 20 of notes, how are reactions of a primary and secondary alcohol different?) propan-2-ol halogenoalkane SOCl2, room temp. Na , room temp. CH3CH2COOH, conc. H 2SO4, heat under reflux or CH3CH2COCl, room temp. K2Cr2O7, H 2SO4 (aq) heat under reflux I2 (aq), NaOH (aq), warm excess conc H2SO4 at 170OC or Al2O3 at 350OC LiAlH4 in dry ether NaOH (aq), heat under reflux steam, 300OC, 60atm, conc H3PO4 or KMnO 4, H 2SO4 (aq), heat under reflux C CH3 Cl CH3 H C CH3 OH CH3 H C CH3 O- Na+ CH3 H CH2 C O O CH CH3 CH3 .CH3 CCH3 O- Na+ O CCH3 CH3 O + CHI3 CC H CH3 H H CC H CH3 H H C CH3 Cl CH3 H CCH3 CH3 O ketone (to learn in Carbonyls)

5 Part 2: Phenols 5 catechol hydroquinone Catechol has a lower melting point (104 oC) than hydroquinone (169 oC). Explain this observation. [3] Both catechol and hydroquinone have simple molecular structure. [1] Both catechol and hydroquinone form intermolecular hydrogen bonds between molecules, but catechol is also able to form intramolecular hydrogen bonds. Formation of intramolecular hydrogen bonds in catechol reduces the extent of intermolecular hydrogen bonding. [1] This leads to weaker intermolecular forces in catechol and therefore less energy is required to overcome these forces. [1] 6 Reversatrol is an insect repellent which is emitted by damaged plants. Which reagent, in its reaction with Reversatrol, shows both electrophilic addition and electrophilic substitution? OH C C H H OH OH A bromine B ethanoyl chloride C hydrogen bromide D steam Ans: A Bromine undergoes electrophilic addition with the alkene and electrophilic substitution on the benzene. (B) Ethanoyl chloride undergoes condensation reaction with the phenol. (C) Hydrogen bromide undergoes electrophilic addition with the alkene. (D) Steam undergoes electrophilic addition with the alkene. OH OH OH OH

6 7 Suggest the condition for the following reagents to react with the compound below, and the organic product(s) obtained. State “no reaction” if they do not react at all. [Hint: Refer to Pg 21 summary by reagent to help recall the different reactions of functional groups] OH CH2OH CH CH2 Reagent Condition Organic product (a) sodium metal room temp O- CH2O - CH CH2 Na + Na + (b) sodium hydroxide room temp O- CH2OH CH CH2 Na + (c) sodium carbonate room temp no reaction (d) phosphorous(V) chloride room temp CH2Cl CH CH2 OH (e) hydrogen bromide heat CH2Br CH OH Br CH2 H It is a good practice to identify the functional gp present in the compound: Phenol, primary alcohol, alkene and arene

7 Reagent Condition Organic product (f) ethanoic acid conc. H2SO4, heat under reflux CH2 CH CH2 OH O C CH3 O (g) anhydrous ethanoyl chloride room temp CH2 CH CH2 O O C CH3 O C CH3 O (h) aqueous bromine room temp OH CH2OH CH Br Br OH CH2 Br Assume excess bromine is provided and phenol undergoes multi-substitution (i) bromine in CCl4 room temp OH CH2OH CH Br Br CH2 Br or OH CH2OH CH Br CH2 Br Br (j) potassium manganate(VII) H2SO4(aq), heat under reflux OH COOH COOH (k) potassium dichromate (VI) H2SO4(aq), heat with immediate distillation OH CHO CH CH2